Neural recording typically selects different parts of the brain to obtain different information. One approach to neural recording includes extra-cellular electrode insertion. Extra-cellular electrode insertion typically involves the insertion of one or more electrodes into neural tissue. Conventional extra-cellular electrode insertion has traditionally followed one of two paths.
One conventional technique extra-cellular electrode insertion is a chronic technique, i.e. long term, such as more than one day. One or more electrodes are surgically implanted in the brain of a subject, such as an animal. In general, these electrodes are not subsequently repositionable without another surgical procedure. Any available motion is typically only in depth. Thus, the X and Y positions along the surface of the brain are fixed during surgery and the Z position into the brain is potentially adjustable. Using this configuration, experimenters can record from a small group of neurons for an extended time period. However, because this technique uses a surgical procedure to insert electrodes into the animal's brain, the experimenters typically can only record from the one collection of neurons corresponding to the surgical site in the animal. To accomplish additional recordings from different collections of neurons in the animal's brain, additional surgical procedures are required for each desired recording site. Due to the trauma of such surgical procedures, test animals typically cannot withstand more than a limited number of applications.
A second conventional technique for extra-cellular electrode insertion is an acute technique, i.e., short term, such as less than one day. This technique typically involves daily reinsertion of electrodes into an animals brain. A craniotomy is opened surgically, and is them covered by an implanted resealable cylinder. This cylinder is typically called a "recording chamber". The recording chamber includes a sealing plug. The sealing plug is used to maintain a closed seal so that intracranial tissue is not exposed while neural recording is not being performed. To perform neural recording, such as on a daily basis, the sealing plug from the recording chamber is removed and one or more electrodes are inserted in a target location in the neural tissue accessed by the craniotomy and defined by the recording chamber. An external device called a "microdrive" is typically used to position the electrodes. The microdrive mounts into the recording chamber and is adjustable in all three dimensions (X, Y, and Z). The microdrive is typically first set to an XY position and then scanned in the Z direction. When neural recording is complete, the microdrive and electrodes are removed from the recording chamber and the sealing plug is replaced, thereby sealing the recording chamber. In this acute technique, the experimenter typically has access to a larger total number of cells than in the chronic technique described above. However, the experimenter typically can record from a given group of cells for at most a single recording session, typically one day. This limitation arises from the exposure of intracranial tissue to an external environment caused by removing the sealing plug of the recording chamber. Prolonged external exposure of the target site tissue is potentially detrimental to the health of the tissue, impeding overall neural recording efficiency.
The inventors have determined that it would be desirable to provide the advantages of chronic neural recording as well as the positional advantages of acute neural recording using a microdrive.